Achieving High Strength and Toughness in Ti6Al4V-Ti Metallic Composite by Engineering 3D Artificial Nacre-Like Structures

Bio-inspired mimicking natural structures generally duplicate the three dimensional “hard brick-and-soft mortar” structure that may overcome the intrinsic brittleness of the brick, resulting in an improved mechanical performance. Here we for the first time propose an anti-bioinspired strategy of designing metallic composite with a soft brick (commercially pure titanium (CP-Ti)) confined by hard mortars (Ti6Al4V alloy), where the three dimensional minority of hard mortar (with a volume fraction of ~14%) was fabricated by using selective laser melting (SLM), and the bricks were introduced by filling in CP-Ti powders followed by the hot isostatic pressing (HIP). The resultant nacre-like structured composite exhibits a periodic distribution of “soft-brick” and “hard-mortar” domains with a remarkable interface between them. This unique structure leads to a combination of high strength and high fracture toughness that both exceed the respective value calculated using the rule of mixtures (ROM). Three dimensional heterogeneous plastic deformation between the two domains induces the mechanical incompatibility, which has been confirmed by the presence of higher density of geometrically necessary dislocations (GNDs) in front of the interface. The large amount of GNDs was believed primarily responsible for the extraordinary strengthening and toughening beyond the ROM. This novel strategy of artificial designing three dimensional “soft brick and hard mortar” structure could be further extended to other metals and alloys, shedding lights on developing new type of heterogeneous materials applicable to industry.